Device for converting an input voltage into an output current or vice versa

ABSTRACT

Device for the distortion-free conversion of a signal voltage into a signal current or vice versa which comprises an input transistor having two main electrodes. A high-resistance current supply source is included between the first main electrode and a supply point, while this main electrode is also connected via a current feedback path to the control electrode of a first transistor the main current path of which is connected in the circuit between the second main electrode of the input transistor and another supply point, the output of the device being a point of the latter circuit.

States Patent 91 Van Kessel et al.

[ DEVICE FOR CONVERTING AN INPUT VOLTAGE lNTO AN OUTPUT CURRENT OR VICE VERSA [75] Inventors: Theodorus- Jozef Van'Kessel; Rudy Johan Van De Plassche; Johannes Otto Voorman, all of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

22 Filed: Jan. 17,1972

21 Appl. No.: 218,389

[30] Foreign Application, Priority Data Feb. 19, 1971 Netherlands 7102199 [52] US. Cl...., 3,07/26 0, 307/235 R, 307/254, 307/270, 307/299, 307/313, 307/297 [58] I Field of Search H03k/3/26; 307/254, 255,

[56] t References Cited UNITED STATES PATENTS 3,1 19,983 .1/1964. Carroll et al 307/254 X 3,287,577 11/1966 Hung et a1. 307/288 X 3,320,439 5/1967 Widlar 307/297 1 July 23, 1974 .Matsuda 307/288 X 3,549,910 12/1970 Ogawa et al. 307/297 X 3,624,426 11/1971 Saari 307/297 3,649,926 3/1972 Hill 330/30 D 3,683,270 8/1972 Mattis 307/270 X OTHER PUBLICATIONS Woodard, Constant Current Source Circuit," IBM Tech. Disc]. BulL, Vol. 13 No. 4, 9/1970, p. 909-910. Wortzman, Current Switch, IBM Tech. Discl. Bull., Vol. 2, No.5, 2/1960, p. 48.

Primary Examinefl-Rudolph V. Rolinec Assistant Examiner-L. N. Anagnos Attorney, Agent, or Firm-Frank R. Trifari 57] ABSTRACT Device for the distortion-free conversion of a signal voltage into a signal current or vice versa which comprises an input transistor having two main electrodes. A high-resistance current supply source is included between the first main electrode and a supply point,

while this main electrode is also connected via a current feedback path to the control electrode of a first transistor the main current path of which is connected in the circuit between the second main electrode of Q the input transistor and another supply point, the output of the device being a point of the latter circuit.

15 Claims, 9 Drawing Figures i i DEVICE FOR CONVERTING AN INPUT VOLTAGE INTO AN OUTPUT CURRENT OR VICE VERSA The invention relates to a device for the substantially distortion-free conversion of a signal voltage into a signal current or vice versa, which device comprises'a first and a second control input and an output for the cur- -the'collector and the second main electrode by the emitter of a transistor. The device has a quiescent current. setting (DC) on which signals may be super.- posed. A voltage is applied to the base of the transistor.

and an output current may' be derived fromthe collec-' tor. .The emitterof the transistor isconnected, for example through a resistor, to a point of constant potential. The output signal current of this device is equal to where i,, is the base signal leakage current of the transistor, R is the resistancevalue of the emitter resistor, V

is "the amplitude of the signal voltage applied to the base of the transistorand V is 'thesignal voltage between the base and the emitter of the transistor. The values of i,, and V,,,. are dependent on the current and on the temperature. This current dependence of V means thatdistor'tion will occur in the output current of the device. Hence the said device is not very suitable for use in highly accurate multipliers and gyrators which have to satisfy stringent quality requirements.

It is an object of the invention to provide a device of the said kind in which a highly accurate voltage to current or current to voltage conversion is effected substantially independently of the transistor parameters andwhich is highly suited'for use in gyrators, multipliers and differential amplifiers.

The invention is characterized in that there is-included in the circuit between the first main electrode and a supply point a high-resistance current source,

' FIG. 6 is a circuit diagramof an alternative output circuit for deriving the output current,

FIG. 7 is a circuit diagram of a further alternative output circuit for deriving the current,

FIG. 8 is a circuit diagram of a symmetrical voltagecontrolled current supply source employing devices according to the invention, and

FIG. 9 is a circuit diagram ofa direct-current supply circuit employing devices according to the invention.

Referring now to FIG. 1, the input electrode of "the device is constituted by the base of a transistor T The first electrode of the transistor T is constituted by its collector and the second electrode by its emitter. The collector of the transistor T o is connected to a supply point of constant potential via a high-resistance to form a current supply source S. The emitter of the transistor T is directly connected to the output C of the device via the collector-emitterpath of a transistor T The base of the transistor T is connected to the collector of the transistor T through the collector-emitter path of a transistor T The base of the transistor T is connected to the emitterof the transistor T and also, through a resistor R, to a point of constant potential.

The operation of the circuit shown in FIG. 1 is as follows. The signal i which will flow through the resistor R as a result of a signal voltage V applied to the base of the transistor T isi= V V /R where R is the resistance value of the resistor R and V I ,i, i i

- If V,,,. V and i,,,, i, the conversion of voltage to the transistor T through the input transistor T V is while furthermore this main electrode is connected, viaa current feedback path, to the control electrode of a first transistor the main current path of which is con-:

nected in the circuit between-the second-main electrode of the input transistor'and another supply point, theoutput being a point of the latter circuit.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a circuit diagram of a first embodiment of the device according to the invention,

FIG. 2 is a circuit diagram'of a second embodiment of the device according to theinvention,

FIG. 3 is a circuit diagram of a third embodiment of small and the leakage current'i also is small, much smaller (-B,x) than if a single transistor were used. The ideal condition i V/R is approximated to with a degree of accuracy higher by a factor of B. The distortion of the signal due to the non-linear characteristics of the transistors is also reduced by a factor of B. Itis tr ue that direct current is supplied to the circuit via the current supply source S, but this source is selected to have so high an impedance that no signal current leaks away. The device T, i.e., the portion of FIG. 1 surrounded by dotted lines, may be regarded as an artificial pnp transistor having a base b, an emitter e and a collector c. The base collector current gain factor of this artificial transistor is about equal to B Its transconductance is about equal to BS, where S is the transconductance of the transistor T,,. The artificial pnp transistor may be used as a high quality direct-current supply source. This is effected by making i= 0, which is the case when the emitter e of the equiv-v alent transistor is floating.- The output direct current then vwill be equal to the direct current supplied by the source S. The resulting direct-current supply source at its output 0 has a very high output impedance which may be of the order of l giga-ohm.

FIG. 2 shows a device for converting an input current into an output voltage in a substantially distortion-free manner. The base 12 of the artificial pnp transistor T is connected to a point of constant potential, for example earth. A signal current i is supplied to the emitter e via a current supply source S,. The collector c of the artificial transistor is connected to a point of constant potential via a resistor R. The operation of the device shown in FIG. 2 is substantially equal to that of the device shown in FIG. 1. A signal current i is supplied to the emitter and a signal voltage substantially equal to iR may be derived from the collector.

The input electrode of the device shown in FIG..3 is constituted by the base of the transistor T The first electrode of the transistor T is constituted by the emitter of this transistor and the second electrode by its collector. The emitter of the transistor T is connected to a constant-potential supply point via a high-resistance to form a current supply source S. The collector of the transistor T, is connected to a supply point of the device via the main current path of a transistor T,. The base of the transistor T is connected to the emitter of the transistor T via the main current path of a transistor T The base of the transistor T is connected to the collector of the transistor T and, via a resistor R, to a point of constant potential. The base of the transistor T is connected to a signal voltage supply source V.

The operation of the device shown in FIG. 3 is as follows.

Owing to the signal voltage V applied to the base b the resistor R will be traversed by a signal current i which is equal to i V V /R where V is the signal voltage between the two control electrodes b and e. The output current of the device may be derived at c and is equal to where l is the signal current which leaks aways through the base of the transistor T Because from the base of the transistor T, only a small part of the main current is fed back via the transistor T and the transistor T,,, i,,,, is very small, as are the base emitter signal voltages of the transistors T and T which together form V,,,. The device T of FIG. 3 may be regarded as an artificial npn transistor with b as the base, e as the emitter and c as the collector. The base-collector current gain factor is about B and the transconductance is about I/[( l/BS) l/BSQ], where S and S, are the transconductances of the transistors T and T respectively. In the same manner as shown in. FIG. 2 with respect to the artificial pnp transistor the artificial npn transistor may be operated in common-base connection. For this purpose the base b is connected'toa point of constant potential. A signal currenti maybe supplied to the emitter e, and the collector c maybe connected toa point ofconstant potential through a re-- sistor. The signal voltage across this resistor then will be substantially iR Volts.

In FIG. 4 the input electrode of the device is constituted by the base of the transistor T,. The first electrode of the transistor T is constituted by the collector of this transistor and the second electrode by its emitter. The collector of the transistor T is connected to a supply point of constant potential via a high-resistance to form a current supply source S. The emitter of the transistor T,, is connected to the output 0 of the device via the main current path of a transistor T,. The base of the transistor T, is connected to the collector of the transistor T via the series combination of diodes D, and D the emitter-base path of a transistor T and the collector-emitter path of a transistor T The second terminal 0 of the device is connected to a highresistance current supply source S, via the collectoremitter path of the transistor T The base of the transistor T is connected to the emitter of the transistor T, and also, via a resistor R, to a point of constant potential. The base of the transistor T, is connected to the high-resistance current supply source S,,. A diode D is connected between the base and the emitter of the transistor T The operation of the circuit shown in FIG. 4 is as follows. The signal current i which flows through the resistor R as a result of a signal voltage V applied to the base of the transistor T satisfies the relationship (2). The transistor T, will pass a collector signal current of (i i,) amperes, where i, is the signal current which largely flows through the emitter-collector path of' the transistor T Because the collector of the transistor T is connected to the high-resistance current supply source S, the signal current i, will also flow through the emittercollector path of the transistor T to the base of the transistor T The collector-emitter path of the transistor T;, will pass a signal i Because the emitter of the transistor T is connected to the high-resistance current supply source S, and because the diode D, is connected to the high-resistance current supply source S,,, the signal current i will flow via the diodes D, and D of the base of transistor T,. We now havejthe following relationships for the currents i, i, and i i, i /B and i z i/B where'B is the collector-base current gain factor of the transistors T,,, T, and T5,. Thus, the signal current flowing through the main current path of the input transistor T is about 1/3 As a result the signal current,

which always goes through the base of the input transistor T,,, will be about i/B, that is smaller by a factor of [3 than in, for example, the device shown in FIG. 1. Consequently the variations in the base-emitter threshold voltage V of the transistor T are reduced by a factor of [3 so that the distortion in the output signal is-about B 8 where S, is the transconductance of the transistor T .In the device shown in FIG. 4 the collector of the first transistor T is connectedto-the, emitter of the input '5 transistor T via the emitter-collectorpath of one transistor. However,the collector of this first transistor may alternatively be connected to theemitter of the input transistor T via the series connection of the emittercollector paths of a plurality (n) of transistors, the base of each of the transistors of the series combination being connected to the emitter of the succeeding transistor via voltage shifting means, while the output of the device then will be constituted by the emitter of that transistor'of the seriesco'mbination which is'connected to the input transistor. If, for example, the emitter of the input transistor isconnected'to a point of constant potential via a resistor and a signalvoltage is applied to the base of the input transistor, the base signal leakage current of the input transistor will be smaller than the signal current passed by the transistor connected to the input transistor by a factor of 3". As a result the distortion in the output signal will be reduced by a factor of B" with respect to the distortion of a single transistor.

The equation-(4) is approximated to with anaccuracy which is [3" times higher.

FIG. shows a differential amplifier employing two artificial pnp-transistors as shown in FIG. 1 The emitters of these artificial pnp-transistors are connected respectively to opposite terminals of a resistor R. A voltv6 improve the high-frequency behaviour of theartificial pnp transistors a diode may be included in-the base circult of the transistor T as is indicated in broken lines in FIGS. 1 and 2, or the emitter-collector path of the transistors T and T 'may each be shunted by a capacitor, as is indicated in broken lines in FIG. 5. The addition'of additional direct current by means of the current supply S (FIGS. landfZ) also improves the highfrequency behaviourtdriving). The diode connected between the emitter and the base of the transistor T (shown in broken lines in FIGS. 1, 2 and 4) improves.

4 the bias setting of the artificial pnp transistor andalso age v is applied between the basesof the artificial pnp-.

transistors. Their collectors are connected to a point of constant potential through D and D 3 respectively. The diodes D and D';. may beidentical transistors, for ex V ample T, and T';,, in which the base and the collector areshort-circuited. The base'of the-transistor T (T is connected to the collector of the' diode'D (D' respectively), while all the four emitters'are connected to one another and to a point of constant potential.- N-ow FIG. 6 shows an alternative embodiment of. the current mirror in which'the transistor T '(T") is combined with the diode D (D respectively). a

FIG. 7 shows a much more accurate alternative em-' bodiment of a current mirror including three transistors in combination with the transistor T In this embodiment serves as a protectionfor the base-emitter diode of the transistor T The differential amplifier shown in FIG. 5 may read-' ily be converted. to a multiplier. For this purpose the emitters of the transistors T and T are connected to a point of constant potential via a common current supply.-

Assuming thesaid current supply tosupply a current of 2I-(l x) amperes and the voltage applied to the input to be Y volts, the output current i contains a component Ixy.

FIG. 8- shows a symmetrical voltage-controlled current supply using twoartificial pnp transistors T and T. The collector c of the equivalent transistorT is con nected via a current supply S 'to a point of constant potential and also via a resistor Z to the collector c of the artificial transistor T. The collector c of the artificial transistor T is also connected to a point of constant povoltage V is applied'between the two base electrodes b The crossing base currents i, and I largely compensate each other. The amplifier of FIG. 5 uses pnp artificial transistors and b of the artificial transistors T and T' respectively an output signal current-will flow through theload impedance 2,, which current is substantially equal to V/R amperes. The two equations"(8) and (9) apply to the currents i and i In the embodiment shown in FIG. 8 two artificial pnp transistors are used. Obviously instead of two artificial pnp transistors two artificial npn transistors as shown, for example, in FIG. 3 may be used. Voltage-controlled current supplies as shown in FIG. 8 enable, for example, the construction of highly accurate gyrators.

The current supply sources S and S used in the embodiment shown in FIG. 8 may be of the type shown in FIG. 9. The current supply shown in FIG. 9 includes an artificial pnp transistor T. The baseof this artificial transistor is connected via the series combination of a.

diode D and a resistor R to a point of constant poten tial U,,*. The base of the artificial pnp transistor T is also connected via a resistor R to another point of constant potential. The emitter of the artificial pnp transistor is floating. From the collector c of the artificial pnp transistor a direct current may be derived which is equal to the direct current passed by the transistor T This current is determined by the current flowing through the branch R D and R and by the value of a resistor R The current supply source shown in FIG. '9 may be used, for example, as the current supply S in FIGS. 1, 2, 4 and 5. In FIG. 4 the currentsupply S may simply be realized by including an additional transistor T in the current supply shown in FIG. 9. The collector of this transistor T isconnected to the base of the transistor T of FIG. 4.

Obviously, the invention is not restricted to the embodiments shown and to one skilled in the art many modifications are possible without departing from the scope of the invention. For example, both bipolar transistors and field-effect transistors may be used. Furthermore field-effect transistors having an n-channel region or'a p-channel region and also both of the enhancement type and of the depletion type may be used.

What is claimed is:

1. A transistor circuit which acts as an artificial transistor having a high B and high transconductance,'comprising:

a high internal resistance constant current supply source;

a first transistor having a base electrode and collector and emitter electrodes forming a first current path;

tor and emitter electrodes forming a third current path, the third current path being electrically connected at one end to the first current path, the base electrode of said third transistor being electrically responsive to .the current flowing in the second path,. 7

whereby the base electrode of said first transistor, the

receiving end of said constant current supply source;

the base electrode of said second transistor is electrically'connected to both the collector electrode of said first transistor and the emitter electrode of said third transistor; and

the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor,

whereby the base electrode of said first transistor, the base electrode of said second transistor and the collector electrode of said third transistor electrically act as if they were base, emitter and collector electrodes respectively of an artificial N PN transistor having a high [3 and a high transconductance.

4. A transistor circuit for substantially distortion-free conversion of a voltage signal into a current signal, comprising a transistor circuit as defined in claim 1 and further comprising:-

a first impedance electrically connected at one end thereof to the base terminal of said second transistor;

a second impedance electrically connected at one end thereof to the other end of the third path; and

a voltage source electrically connected between the other ends of said first and second impedances, whereby a voltage signal applied to the base terminal of said first transistor is converted into a proportionate substantially distortion-free current signal through said second impedance.

base electrode of said second transistor and the other end of the third current path electrically act as if they were base, emitter and collector electrodes respectively of an artificial transistor having a high B and high transconductance.

2. A transistor circuit as defined in claim 1 wherein: said first and third transistors are of NPN type and said second transistor is of PNP type; i

the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said constant current supply source; the base electrode of said second transistor is electrically connected to both the emitter'electrode of said first transistor and the collector electrode of said third transistor; and the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor, whereby .the base electrode of said first transistor, the base electrode of said second transistor andthe emitter electrode of said third transistor electrically act as if they were base, emitter and collector electrodes respectively of an artificial PNP transistor having ahigh B and high transconductance.

3. A transistor circuit as defined in claim 1 wherein:

said first, second and third transistors are of NPN type;

the emitter electrodes of said first and second transistors are both electricallyconnected to the current 5. A transistor circuit as defined in claim 4 wherein:

said first and third transistors are of NPN type and said second transistor is of PNP type;

the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said constant current supply source;

the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor;

thecollector electrode of said second transistor is electrically connected to the base electrode of said third transistor;

said second impedance is electrically connected at one end thereof to the emitter electrode of said third transistor; and

said voltage source is electrically connected between said impedances with the side of more negative potential connected to said second impedance.

6. A transistor circuit as defined in claim 4 wherein:

said first, second andsthird transistors are of NPN the emitter electrodes of said first and second transistors are both electrically connected to the current receiving end of said constant current supply source;

the base electrode of said second transistor is electrically connected to both the collector electrode of said first transistor and the emitter electrode of said third transistor;

the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor;'

one end thereof to the collector electrode of said third transistor; and said voltage source is electrically connected between said impedances with the side of more positive potential connected to said second impedance. 7.'A-transistor circuit for substantially distortion-free conversion of a current signal into a voltage signal,

comprising a transistor circuit as defined in claim 1 and further comprising:

animpedance electrically connected at one end thereof to the other end of the third path; and a voltage source electrically connected between the base electrode of said first transistor and the other end of said impedance, whereby a current signal applied to the base terminal of said second transistor is converted into a proportional substantially distortion-free voltage signal across said impedance.

8. A transistor circuit as defined in claim 7 wherein:

said first and third transistors are of NPN type and said second transistor is of PNP type; v

the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end 'of said constant current. supply source;

the base electrode of said second transistor is electrically connectedto both the emitter electrode of said first transistor and the collector electrode of said third transistor the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor; I g

said impedance is electrically connected at one end thereof to the emitter electrode of said third transistor; and.

said voltage source is electrically connected between the base electrode of said first transistor and the other end of said impedance with the side of more negative potential connected to said impedance.

9. A transistor circuit as defined in claim 1 and fur,-

ther comprising: p

a fourth transistor having abase electrode and collector and emitter electrodes forming a fourth current path, the fourth current path being electrically connected at one end thereof to the other end of the third current path;

two diodes electrically connected in series between the base electrode of said third transistor and the other end of said fourth current path;

a second high internal resistance constant current I supply source connected at one end thereof to the other end of the fourth current path; and

a third high internal resistance constant current supply source connected at one-end thereof to the base electrode of said third transistor, the second and third constant current supply sources biasing said third and fourth transistors without thereby shunting signal current therefrom, the base electrode of said fourth transistor being electrically responsive to the current flowing in the second path,

whereby the base electrode of said first transistor, the

base electrode of said second transistor and the other end ofthe third current path electrically act as if they were base, emitter and collector electrodes respectively of an artificial transistor having a high H and big transconductance.

10. A transistor circuit as defined in claim 9 wherein:

said first, third and fourth transistors are of NPN type and said secondtransistor is of PNP type;

the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said first constant current supply source;

the base electrode of said second transistor is electrically connected to both the emitter electrode of saidfirst transistor and the collector electrode of said third transistor; v

the emitter electrode of said third transistor is electrically connected to the collector electrode of said fourth transistor;

the emitter electrode of said fourth transistor and the emitter side of said series connected diodes are both electrically connected to the current receiving end of said second constant current supply source;

the base electrode of said third transistor and the collector side of said series connected diodes are both electrically connected to the current supplying end of said third constant currentsupply source; and the collector electrode of said second transistor is electrically connected to the base electrode of said fourth transistor, whereby the base electrode of said first transistor, the base electrode of said secondtransistor and the emitter electrode of said third transistor electrically act as if they were base, emitter and collector electrodes respectively of an artificial PNP transistor having a high B and high transconductance.

l1. A transistor circuit for substantially distortionfree conversion of a voltage signal into a current signal, comprising a transistor circuit as defined in claim 9 and further comprising:

a first impedance electrically connected at one end thereof to the base terminal of said second transistor; r

a second impedance electrically connected at one end thereof to the other end of the third path; and

a voltage source electrically connected between the other ends. of said first and second impedances, whereby a voltage signal applied to the base terminal of said first transistor is converted into a proportionate substantially distortion-free current signal through said second impedance.

12. A transistor circuit as defined in claim 11 wherein: v

said first, third and fourth transistors are of NPN type and said second transistor is of PNP type; the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said first constantcurrent supply source; the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor; the emitter electrode of said third transistor is electrically-connected to the collector electrode of said fourth transistor;

the emitter electrode of said fourth transistor and the emitter side of said series connected diodes are both electrically connected to the current receiving end of said second constant current supply source;

said impedances with the side of more negative potential connected to said second impedance.

13. A transistor circuit as defined in claim 1 and further comprising a high internal resistance constant current supply source electrically connected at one end thereof to the other end of the second current path.

14. A transistor circuit as defined in claim 1 and further'comprising a diode electrically connected between the base electrode of said first transistor and the base electrode of said second transistor.

15. A transistor circuit as defined in claim 1 and further comprising a capacitance electrically connected from the emitter terminal of said second transistor to the collector terminal thereof.

UNITED STATES ATENT 0mm THIQME Patent No. 3,825, 774- Dated uly 23,1974

Inventofls) Theodorus Jozef Van Kessel et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cola line 25, the formula shoulo'l road ""i R i-b Col, 2, line 29, the formula should read? --i= (V V )/R-=--=- Col, 3, line 38,, the formula should read --i= (v V )/R Q01. 5, line 37, the formula should read --i= (V '-2v )R-- Col. 5, line 46, "D T should be --D T Signed and sealed this 22nd day of October 1974.

(SEAL) Attest:

MccorM. GIBSON JR, c MARSHALL DANN Arrest-111g Offmer Goissioner of Patents 

1. A transistor circuit which acts as an artificial transistor having a high Beta and high transconductance, comprising: a high internal resistance constant current supply source; a first transistor having a base electrode and cOllector and emitter electrodes forming a first current path; a second transistor having a base electrode and collector and emitter electrodes forming a second current path, the first and second current paths being electrically connected at one end thereof to said constant current supply source to maintain currents through the first and second current paths the sum of which always totals the current maintained by said constant current supply source, the other end of the first current path being electrically connected to the base electrode of said second transistor; and a third transistor having a base electrode and collector and emitter electrodes forming a third current path, the third current path being electrically connected at one end to the first current path, the base electrode of said third transistor being electrically responsive to the current flowing in the second path, whereby the base electrode of said first transistor, the base electrode of said second transistor and the other end of the third current path electrically act as if they were base, emitter and collector electrodes respectively of an artificial transistor having a high Beta and high transconductance.
 2. A transistor circuit as defined in claim 1 wherein: said first and third transistors are of NPN type and said second transistor is of PNP type; the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said constant current supply source; the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor; and the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor, whereby the base electrode of said first transistor, the base electrode of said second transistor and the emitter electrode of said third transistor electrically act as if they were base, emitter and collector electrodes respectively of an artificial PNP transistor having a high Beta and high transconductance.
 3. A transistor circuit as defined in claim 1 wherein: said first, second and third transistors are of NPN type; the emitter electrodes of said first and second transistors are both electrically connected to the current receiving end of said constant current supply source; the base electrode of said second transistor is electrically connected to both the collector electrode of said first transistor and the emitter electrode of said third transistor; and the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor, whereby the base electrode of said first transistor, the base electrode of said second transistor and the collector electrode of said third transistor electrically act as if they were base, emitter and collector electrodes respectively of an artificial NPN transistor having a high Beta and a high transconductance.
 4. A transistor circuit for substantially distortion-free conversion of a voltage signal into a current signal, comprising a transistor circuit as defined in claim 1 and further comprising: a first impedance electrically connected at one end thereof to the base terminal of said second transistor; a second impedance electrically connected at one end thereof to the other end of the third path; and a voltage source electrically connected between the other ends of said first and second impedances, whereby a voltage signal applied to the base terminal of said first transistor is converted into a proportionate substantially distortion-free current signal through said second impedance.
 5. A transistor circuit as defined in claim 4 wherein: said first and third transistors are of NPN type and said second transistor is of PNP type; the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said constant current supply source; the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor; the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor; said second impedance is electrically connected at one end thereof to the emitter electrode of said third transistor; and said voltage source is electrically connected between said impedances with the side of more negative potential connected to said second impedance.
 6. A transistor circuit as defined in claim 4 wherein: said first, second and third transistors are of NPN type; the emitter electrodes of said first and second transistors are both electrically connected to the current receiving end of said constant current supply source; the base electrode of said second transistor is electrically connected to both the collector electrode of said first transistor and the emitter electrode of said third transistor; the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor; said second impedance is electrically connected at one end thereof to the collector electrode of said third transistor; and said voltage source is electrically connected between said impedances with the side of more positive potential connected to said second impedance.
 7. A transistor circuit for substantially distortion-free conversion of a current signal into a voltage signal, comprising a transistor circuit as defined in claim 1 and further comprising: an impedance electrically connected at one end thereof to the other end of the third path; and a voltage source electrically connected between the base electrode of said first transistor and the other end of said impedance, whereby a current signal applied to the base terminal of said second transistor is converted into a proportional substantially distortion-free voltage signal across said impedance.
 8. A transistor circuit as defined in claim 7 wherein: said first and third transistors are of NPN type and said second transistor is of PNP type; the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said constant current supply source; the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor; the collector electrode of said second transistor is electrically connected to the base electrode of said third transistor; said impedance is electrically connected at one end thereof to the emitter electrode of said third transistor; and said voltage source is electrically connected between the base electrode of said first transistor and the other end of said impedance with the side of more negative potential connected to said impedance.
 9. A transistor circuit as defined in claim 1 and further comprising: a fourth transistor having a base electrode and collector and emitter electrodes forming a fourth current path, the fourth current path being electrically connected at one end thereof to the other end of the third current path; two diodes electrically connected in series between the base electrode of said third transistor and the other end of said fourth current path; a second high internal resistance constant current supply source connected at one end thereof to the other end of the fourth current path; and a third high internal resistance constant current supply source connected at one end thereof to the base electrode of said third transistor, the second and third constant cUrrent supply sources biasing said third and fourth transistors without thereby shunting signal current therefrom, the base electrode of said fourth transistor being electrically responsive to the current flowing in the second path, whereby the base electrode of said first transistor, the base electrode of said second transistor and the other end of the third current path electrically act as if they were base, emitter and collector electrodes respectively of an artificial transistor having a high Beta and high transconductance.
 10. A transistor circuit as defined in claim 9 wherein: said first, third and fourth transistors are of NPN type and said second transistor is of PNP type; the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said first constant current supply source; the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor; the emitter electrode of said third transistor is electrically connected to the collector electrode of said fourth transistor; the emitter electrode of said fourth transistor and the emitter side of said series connected diodes are both electrically connected to the current receiving end of said second constant current supply source; the base electrode of said third transistor and the collector side of said series connected diodes are both electrically connected to the current supplying end of said third constant current supply source; and the collector electrode of said second transistor is electrically connected to the base electrode of said fourth transistor, whereby the base electrode of said first transistor, the base electrode of said second transistor and the emitter electrode of said third transistor electrically act as if they were base, emitter and collector electrodes respectively of an artificial PNP transistor having a high Beta and high transconductance.
 11. A transistor circuit for substantially distortion-free conversion of a voltage signal into a current signal, comprising a transistor circuit as defined in claim 9 and further comprising: a first impedance electrically connected at one end thereof to the base terminal of said second transistor; a second impedance electrically connected at one end thereof to the other end of the third path; and a voltage source electrically connected between the other ends of said first and second impedances, whereby a voltage signal applied to the base terminal of said first transistor is converted into a proportionate substantially distortion-free current signal through said second impedance.
 12. A transistor circuit as defined in claim 11 wherein: said first, third and fourth transistors are of NPN type and said second transistor is of PNP type; the collector electrode of said first transistor and the emitter electrode of said second transistor are both electrically connected to the current supplying end of said first constant current supply source; the base electrode of said second transistor is electrically connected to both the emitter electrode of said first transistor and the collector electrode of said third transistor; the emitter electrode of said third transistor is electrically connected to the collector electrode of said fourth transistor; the emitter electrode of said fourth transistor and the emitter side of said series connected diodes are both electrically connected to the current receiving end of said second constant current supply source; the base electrode of said third transistor and the collector side of said series connected diodes are both electrically connected to the current supplying end of said third constant current supply source; the collector electrode of said second transistor is electrically connected to the base electrodE of said fourth transistor; said second impedance is electrically connected at one end thereof to the emitter electrode of said third transistor; and said voltage source is electrically connected between said impedances with the side of more negative potential connected to said second impedance.
 13. A transistor circuit as defined in claim 1 and further comprising a high internal resistance constant current supply source electrically connected at one end thereof to the other end of the second current path.
 14. A transistor circuit as defined in claim 1 and further comprising a diode electrically connected between the base electrode of said first transistor and the base electrode of said second transistor.
 15. A transistor circuit as defined in claim 1 and further comprising a capacitance electrically connected from the emitter terminal of said second transistor to the collector terminal thereof. 